Essential oils from herbs and spices of the Lamiaceae family increasingly are being used as antioxidants. In addition, essential oils from several herbs have antimicrobial properties. Among the secondary metabolites found in essential oils from Lamiaceae plants, rosmarinic acid (.alpha.-O-caffeoyl-3,4-dihydroxy-phenyllactic acid) is one of the most abundant.
Among various Lamiaceae herbs and spices, oregano is an important plant widely used in South European cuisine. Essential oils obtained from oregano have antioxidant activity. Antioxidant activity was observed when essential oils from oregano were added to lard, salad dressing, or model food systems. Among the secondary metabolites found in oregano are carvacrol, thymol, and rosmarinic acid, which appear to be important for antioxidant activity. Thymol and carvacrol also have antimicrobial activity.
Essential oils from thyme (Thymus vulgaris L) have antioxidant properties and it is suspected that these may result from the presence of free radical scavengers in these oils. The antioxidant property of essential oils of thyme has been correlated with phenolic secondary metabolites such as thymol and carvacrol. In addition, these compounds have been shown to have bactericidal and fungicidal properties. These essential oils are sources of natural preservatives for a variety of food and medical applications.
Rosemary (Rosmarinus officinalis) is a member of the family Lamiaceae. The major commercial sources of rosemary are from diverse global markets; most of the processing of rosemary into extracts and the use of such extracts is carried out in developed countries. The essential oil of rosemary is presently used in flavor preparations, perfumery, and medicine. Rosemary extracts contain a large number of compounds, including carnosic acid, carnosol, and rosmarinic acid.
Oregano, thyme, rosemary, sage, holy basil, mint, and other plants in the family Lamiaceae (formerly Labiateae) are naturally cross-pollinating species and, therefore, populations are genetically heterogeneous. This heterogeneity results in significant variation in secondary metabolite content in such populations.
Current breeding and selection methods for Lamiaceae are not as well developed as methods for many other plants. Therefore, there is considerable variation in the secondary metabolite levels in essential oil extracts from such plants, even when extracts are obtained from the same source or production region.
To improve ingredient quantity and uniformity it would be useful to develop elite plant varieties with uniform genetic backgrounds. This process generally is difficult using traditional plant breeding techniques due to insufficient knowledge concerning the genetics of secondary metabolism in Lamiaceae and the high degree of heterogeneity in populations of Lamiaceae species.